Silicate-containing antifog coatings

ABSTRACT

A coating composition comprising an alkali metal silicate, a wetting agent, and a hydrophilic antifog agent forms an antifog coating on a substrate. The coating may be applied to the surface of a film from an aqueous dispersion of the ingredients, followed by drying to form a composite film.

This application is a national phase filing of PCT Application No. U.S.09/034,358, filed 18 Feb. 2009, and claims priority of U.S. provisionalApplication No. 61/066,543, filed 21 Feb. 2008, the entireties of whichapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Glass or plastic materials used for windows, mirrors, lenses, goggles,and facial masks or shields become foggy when they are exposed to highhumidity and temperature, or used at interfacial boundaries with a largedifference in temperature or humidity. Products exposed to suchconditions include those used in medical, military and industrial safetyapplications. Fog is caused by the condensation of moisture on thesurface. For example, exhaled air from a person wearing a safety shieldcould cause fogging. To reduce or eliminate this problem, antifogcoatings are frequently needed.

Antifog coatings may also be needed for use on disposable items such assingle-use facemasks, which typically are based on polymer filmsubstrates. For these and other applications, it is desirable that costbe kept to a minimum, and therefore in-line application methods would inmany cases be desirable in order to keep costs low. However, existingantifog compositions capable of providing suitable antifog propertiesare often not easily applied by in-line processes. There is a continuingneed for antifog coatings, and methods of applying them, capable ofaddressing these needs.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a composite film including apolyester film substrate having first and second sides, and on at leastone of those sides a coating composition including an alkali metalsilicate, a wetting agent, and a hydrophilic antifog agent.

In another aspect, the invention provides a method of making a compositefilm. The method, includes the steps of:

a) providing an unoriented or monoaxially oriented polyester filmsubstrate having first and second sides;

b) forming on at least one of the first and second sides a layer of acoating composition including an alkali metal silicate, a wetting agent,and a hydrophilic antifog agent, the forming including contacting the atleast one side with a dispersion of the composition in an aqueousdiluent and then evaporating the diluent; and

c) subsequent to step b), stretching the unoriented or monoaxiallyoriented polyester film substrate to respectively monoaxially orbiaxially orient the substrate.

In still another aspect, the invention provides a polymeric or glassarticle having on a surface thereof a coating composition including analkali metal silicate, a wetting agent, and a hydrophilic antifog agent.

In a further aspect, the invention provides a formulation including, inan aqueous diluent, a dispersion of a composition including an alkalimetal silicate, a wetting agent, and a hydrophilic antifog agent.

In a still further aspect, the invention provides a film including analkali metal silicate, a wetting agent, and a hydrophilic antifog agent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides polyester films bearing on their surfacean antifog composition. Depending on the intended application for thepolyester film, the coating may be applied to one or both sides of thefilm. If both sides are coated, the to same composition will typicallybe used for both, although different ones may be used.

As will be discussed in detail further below, antifog coatingcompositions may be applied by in-line or off-line processes, with theformer being preferred in some embodiments. However, the studies leadingup to this invention revealed that traditional formulations for formingantifog coatings are often not suitable for is application prior to asubsequent draw step (for example, during the interdraw phase, i.e.,between a first and a second drawing step) in an in-line process,because the draw results in crazes and/or cracks in the coating. Thisresults in deteriorated optical properties. The compositions describedherein may be used for either type of coating process without crackingor crazing, and thus represent a significant advance in antifog coatingtechnology. Further, the resulting coatings may be quite thin, allowingadditional cost reduction.

Although one particularly useful application of the coating compositionsof this invention is for coating films, the compositions may be appliedto the surface of any article. Polymeric or glass articles may be ofparticular utility, especially if they are transparent. Exemplary glassarticles include films, sheets/plates, mirrors, and eyeglasses or otheroptical devices. Aqueous dispersions of the compositions, and driedfilms made from the compositions, are also embodiments of the inventionwithout respect to whether they are in the form of coatings on asubstrate.

Coating compositions useful for practicing the invention will now bedescribed with respect to the ingredients that are used to prepare them.The skilled artisan will be aware that a variety of chemical reactions(for example, crosslinking) may occur between the various componentseither before or after application and drying, and accordingly whencompositions are described they are meant to refer both to theingredients themselves and to the products of such reactions, if any.The term “active ingredients” will mean all ingredients other than wateror other volatile diluent.

Antifog Coating Compositions

Coating compositions according to the invention contain an alkali metalsilicate, a wetting agent, and a hydrophilic antifog agent. Typically,these are dispersed in a volatile carrier such as water, which may(except for the possible addition of small amounts of other additives)constitute the balance of the composition.

The alkali metal silicate is typically potassium silicate. However, insome embodiments, sodium silicate may be used to partially or completelyreplace potassium silicate. Alkali metal silicates are widely availablefrom a variety of commercial suppliers such as Ineos Silica Ltd. ofWarrington, Cheshire, UK. The alkali metal silicate will typically bepresent in at least a 0.025 wt % level, and more typically at least 0.05wt %. Typically, it will be at most 0.25 wt %, and more typically atmost 0.15 wt %.

Other exemplary wetting agents include RENEX® 690 Polyoxyethylene (10)nonylphenol From Uniqema, CAFLON® NP10 isononylphenyl ethoxylate fromUnivar Ltd., and fluorosurfactants such as ZONYL® FSN, FS-500, FS-510,FSO, FSE, FS610 etc. surfactants from DuPont and Lodyne® S-110, S-152Betc. surfactants from Ciba Specialty Chemicals.

Suitable wetting agents also include any of a variety of polysiloxane-or silicone-based surfactants, including those bearing polyether (e.g.,polyoxyalkylene) substituents. These include nonionic varieties such asTEGO-WET® 251 polyether modified polysiloxane surfactant (Tego ChemieService GmbH, Division of Degussa, Essen, Germany. The wetting agentwill typically be present in at least a 0.2 wt % level, and moretypically at least 0.4 wt %. Typically, it will be at most 2 wt %, andmore typically at most 1 wt %.

Suitable hydrophilic antifog agents include GLYCOLUBE® AFA-1 mixture oftriglyceryl monooleate, sorbitan monooleate ethoxylate, and glycerinefrom Lonza, Inc. (Fair Lawn, N.J.); and sodium alkyl sulfates such asWITCOLATE™ WAQE sodium lauryl sulfate (Akzo Nobel IndustrialSpecialties, Chicago, Ill.); and BYK® 302, 333 and 348 polyethermodified dimethylpolysiloxane copolymers (BYK Additives & Instruments46483 Wesel, Germany). Typically, the antifog agent has a molecularweight M_(n) of at most 20,000 Daltons, and usually it is water-soluble.In some embodiments of the invention, the hydrophilic antifog agent is acompound having three or more polyoxyethylene chains, typicallyOH-terminated on one end, wherein the oxyethylene content is at least 45wt %. Typically, it is at least 55 wt %, and more typically at least 65wt %. Examples include certain fatty acid monoesters of sorbitanethoxylates such as TWEEN®20 polyoxyethylene (20) sorbitan monolaurate(Uniqema, New Castle, Del.). The hydrophilic antifog agent willtypically be present in at least a 0.2 wt % level, and more typically atleast 0.4 wt %. Typically, it will be at most 2 wt %, and more typicallyat most 1 wt %.

In some embodiments of the invention, a small amount of a particulateantiblocking agent may be added to the formulation. Exemplaryantiblocking agents include crosslinked particulate acrylic (co)polymerssuch as those sold by Esprix Technologies (Sarasota, Fla.) under thenames MX-150, XX-1255Z, and XX-1269Z. If used, the particulateantiblocking agent will typically be present in the composition in anamount of from about 0.01 wt % to about 0.1 wt %, with 0.05 wt % moretypically being the upper limit.

In some embodiments of the invention, it is desired that the coatedsubstrate be clear and colorless. In such cases, the coatingcompositions are essentially free of colorants, dyes, pigments,opacifiers, silver halides, fluorescent or phosphorescent additives,particulate materials, or other materials that significantly affecttransparency, color or the like so as not to defeat the purposes of theinvention. In some embodiments, the compositions are essentially free ofsilica particles, including colloidal and precipitated silica particles,and/or essentially free of tetraalkyl orthosilicates or hydrolysisproducts thereof.

In some embodiments of the invention, it is desired that the coatedsubstrate be free of any material that might result in image formation,such as photosensitizers, photo-activated catalysts, andphotopolymerizable or crosslinkable monomers, oligomers, or polymers. Insome embodiments, the compositions exclude species (e.g., oligomers orpolymers) having a molecular weight M_(n) greater than 20,000 Daltons.In some embodiments, either or both of the wetting agent and thehydrophilic antifog agent are nonionic, and the compositions areessentially free of anionic or cationic surfactants or polymers.

In some embodiments, any or all of the following classes of polymericmaterial may be undesirable in certain situations and thus may beexcluded from the compositions: polyethylene oxides, polyethyleneglycols, polymers with multiple sulfonic groups, polyesters, acrylamide(co)polymers, acrylate salt or ester (co)polymers, N-vinylpyrrolidone(co)polymers, vinyl alcohol (co)polymers, polyurethanes, polyureas,cellulose esters or ethers, epoxide-containing resins, and gelatins.

Coating compositions according to the invention will typically beapplied as a dispersion in a volatile diluent, which may include asolvent. In most cases, the diluent will be aqueous, which as usedherein means that the diluent is at least 50 wt % water. In someembodiments, the aqueous diluent is at least 90 wt % water, and in manycases it will be 100 wt % water. Such dispersions will typically havetotal solids in a range from 0.5 to 15 wt %, and more typically in arange of 2 to 5 wt %. As is well known to those skilled in the art,“total solids” refers to the amount of non-volatile material present inthe coating composition even though some of the non-volatile materialpresent may be a liquid at room temperature.

The viscosity of the dispersed coating composition will typically be ina range from 1 to 100 Pas for gravure-type coating methods, but can begreater than 100 Pas for other coating methods. In addition, it isdesirable that the functional components are compatible with each otherto allow dispersed coating composition to be stable in storage and alsostable to the conditions (such as high shear) of coating techniques towithout particle flocculation, aggregation, crystallization, or otherdeterioration in properties.

Preparation of Composite Films

Any polymer, typically in the form of a film, is suitable for use as asubstrate according to the invention. Thermoplastic polymers aretypically used. Non-limiting is examples include polyesters, such aspolyethylene terephthalate or polybutylene terephthalate; polyacrylates,such as polymethylmethacrylate; polystyrenes or acrylate copolymers;nylon; polybutyrate; polypropylene; polyethylene; polybutene; olefincopolymers; polycarbonate; and polyacrylonitrile.

The polymeric film may also comprise a polyarylether or thio analoguethereof, particularly a polyaryletherketone, polyarylethersulphone,polyaryletheretherketone, polyaryletherethersuiphone, or a copolymer orthio analogue thereof. Examples of these polymers are disclosed inEP-A-1879, EP-A-184458 and U.S. Pat. No. 4,008,203. The polymeric filmmay comprise a poly(arylene sulphide), particularly poly-p-phenylenesulphide or copolymers thereof. Blends of the aforementioned polymersmay also be employed.

Suitable thermoset resin polymeric materials may also be used assubstrates according to the invention. Examples includeaddition-polymerization resins such as acrylics, vinyls, bis-maleimidesand unsaturated polyesters; formaldehyde condensate resins such ascondensates with urea, melamine or phenols; cyanate resins;functionalised polyesters; and polyamides or polyimides.

The substrate may in some embodiments be a multi-layer film. Forexample, the film may comprise a base layer such as polyethyleneterephthalate and a heat-sealable layer provided thereon. Such aheat-sealable layer may be provided by coating from a solvent, or by anyother means. In some embodiments, it is effected by coextrusion, eitherby simultaneous coextrusion of the respective film-forming layersthrough independent orifices die, and thereafter uniting the stillmolten layers, or preferably, by single-channel coextrusion in whichmolten stream of the respective polymers are first united within achannel leading to a die manifold, and thereafter extruded together froma die orifice under conditions of streamline flow without intermixing toproduce a multi-layer polymeric film, which may be oriented and heat-setas described previously herein.

In some embodiments of the invention, the substrate includes acrystalline polyester prepared from the polycondensation of one or moreglycols or diols (such as ethylene or propylene glycol or butane diol)with one or more diacids or esters (typically methyl esters) thereof.Suitable diacids include terephthalic acid, naphthalene dicarboxylicacid, isophthalic acid, diphenic acid and sebacic acid. Exemplarypolyester films useful in the present invention include polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polypropyleneterephthalate, and polybutylene terephthalate, or mixtures of these, orcopolyester films in which any one of the above mentioned polyesters ispresent. For example, a film of polyethylene terephthalate/isophthalate(PETIP) copolyester may be used according to the invention. Anothersuitable example is film made from a copolyester of PET and PEN.Typically, PET will be used.

In the typical manufacture of polyester film, polyester resin is meltedand extruded as an amorphous sheet onto a polished revolving castingdrum to form a cast sheet of the polymer. Thereafter, the cast sheet ofpolymer is heated to just above its glass transition temperature, 80° C.to 100° C. for polyethylene terephthalate, and is generally stretched ordrawn in one or more directions. Typically it is stretched in twodirections: the direction of extrusion (longitudinal direction), andperpendicular to the direction of extrusion (transverse direction) toproduce a biaxially orientated film. The first stretching, which impartsstrength and toughness to the film, conventionally increases theoriginal length of the film by a factor of from about 2.0 to about 4.0.Subsequent stretching steps each also increase the size of the filmabout 2.0 to about 4.0 times. Generally, it is preferred to stretchfirst in the longitudinal direction and then in the transversedirection. The film is then heat set, generally at a temperature in therange of about 190° C. to 240° C. for polyethylene terephthalate, tolock in the strength, toughness, and other physical properties, and thencooled down prior to winding on a roll.

The present invention adds to this process a step of coating thesubstrate with an antifog composition on one or both sides of the filmsubstrate. In the case of a polyester, a number of suitable ways ofdoing this may be used. The process for coating the antifog compositionmay be conducted either in-line or off-line. All processes involve afinal cooldown step, and as used herein, the term “in-line” refers to acoating process that is performed at any point prior to the finalcooldown step, and an “off-line” coating process is one in which thecoating step is conducted afterward. Nonlimiting examples of usingin-line coating processes to make coated films according to theinvention will now be presented, using PET as an exemplary polyester.

In a first embodiment of the invention, PET is dried and thenmelt-extruded into a flat sheet and cooled on a chilled roll or drum toform a substrate layer. The temperature of the cast film is thenincreased by passing the film over hot rollers (80° C.-85° C.) andheating by infrared heaters. The film is then stretched lengthwise at adraw ratio of 3.4:1. The stretched film is then contacted with chilledrolls (15° C.-25° C.), which reduces the film temperature to minimizecrystallization and embrittlement of the film. The film is then coatedon one or both sides with the antifog coating solution. Any suitableroll coating method may be used, or other coating method. The coatedfilm is dried in a tenter frame in two forced air ovens at about 105° C.The film is then drawn in the transverse direction at a ratio of 3.0:1to 4.5:1 in two ovens operating at 110° C.-130° C. After drawing, thecoated film is heat set for about 8 seconds in three heat-setting ovensoperating at between 225° C. and 237° C. In a final cooldown step, thefilm temperature is reduced in an air oven operating at about 165° C.

In another embodiment of the invention, PET is melt-extruded into a flatsheet, cooled on a chilled roll or drum, and passed over hot rollers andheated by infrared heaters as described in the first embodiment. Thefilm is then coated on one or both sides with the antifog coatingsolution, and then dried in a tenter frame in two forced air ovens atabout 105° C. The film is then drawn in both lengthwise and transversedirection at a ratio of 2.0:1 to 5.0:1 in ovens operating at 110°C.-130° C. After drawing, the coated film is heat set and cooled down asdescribed in the first embodiment.

In yet another embodiment of the invention, the process of the firstembodiment is repeated but without the transverse drawing step, therebyproducing a uniaxially drawn product.

In still another embodiment, the process of the first embodiment isrepeated except that the transverse drawing step is replaced by a secondlengthwise draw in two ovens operating at 110° C.-130° C. at a drawratio of 3.0:1 to 4.5:1, thereby producing a monoaxially drawn product.

Any conventional coating method, such as spray coating, roll coating,slot coating, meniscus coating, immersion coating, wire-bar coating, airknife coating, curtain coating, doctor knife coating, direct and reversegravure coating, and the like, may be used to apply the coatingcomposition. The coating is typically applied as a continuous wetcoating having a thickness in a range from 1.0 to 30 microns, and moretypically in a range of 5 to 20 microns, as measured by a wet infraredgauge. After drying, the coating typically has a thickness in a rangefrom 0.025 to 1.5 microns, and more typically in a range of 0.060 to0.16 microns.

In other embodiments of the invention, a conventional off-line coatingprocess may be used, using any of the wide variety of coating methodsknown in the art. However, the ability to use in-line coating confersadvantages of economy and efficiency over off-line processes (in whichthe coating step could typically only be conducted after the manufactureof the polyester substrate has been completed) because off-lineprocesses may involve organic solvents and/or require the user to employinconvenient and costly drying procedures. In contrast, in-line coatingby the manufacturer provides a customer with a ready-to-use film,thereby saving the customer from having to provide time and equipment tounwind the uncoated film, coat it, and then rewind it.

If an in-line process is used, the coating composition is typicallyapplied before final drawing of the film. For a uniaxially drawn film,the coating composition is preferably applied after drawing. For abiaxially or monoaxially orientated film, the coating composition istypically applied during an interdraw stage, that is, after the film hasalready been stretched but prior to a second stretching.

In some embodiments, one or (more typically) both sides of the substratemay be coated with a “slip coating” comprising a particulate material inorder to assist in the handling of the film, for instance to improvewindability and minimize or prevent “blocking”. Such a coating may forexample be applied in-line after film orientation and before finalwinding. The slip coating may be applied to either side of thesubstrate, or both. Suitable slip coatings may comprise potassiumsilicate, such as that disclosed in, for example, U.S. Pat. Nos.5,925,428 and 5,882,798, the disclosures of which is incorporated hereinby reference. Alternatively, a slip coating may comprise a discontinuouslayer of an acrylic and/or methacrylic polymeric resin optionallyfurther comprising a cross-linking agent, as disclosed in, for example,EP-A-0408197.

EXAMPLES Glossary

The following materials are referred to in the Examples, and areidentified here.

K120 potassium silicate solution from INEOS Silica, Ltd. (Warrington,Cheshire, UK) 52% active

GLYCOLUBE® AFA-1 mixture of triglyceryl monooleate, sorbitan monooleateethoxylate, and glycerine from Lonza, Inc. (Fair Lawn, N.J.), 100%active

TEGO-WET® 251 polyether modified polysiloxane surfactant (Tego ChemieService GmbH, Division of Degussa, Essen, Germany), 100% active

MX-150 Solid particulate crosslinked acrylic copolymer from EsprixTechnologies (Sarasota, Fla.), used as 100% active

XX-1255Z Solid particulate acrylic polymer dispersion from EsprixTechnologies (Sarasota, Fla.), used as 20% active

XX-1269Z Solid particulate acrylic polymer dispersion from EsprixTechnologies (Sarasota, Fla.), used as 20% active

BYK® 348 polyether modified dimethylpolysiloxane copolymer (BYK-ChemieUSA Wallingford, Conn.), 100% active

MAZOL® GMO K Kosher glycerol Monooleate (BASF, Mt. Olive, N.J.), 100%active

Poly(acrylamide-acrylic acid, Na salt) 40% carboxyl 2-propenoic acid,sodium salt, polymer with 2-propenamide (Polysciences, Inc., Warrington,Pa.), 100% active

PRIMAFLO® HP22 polymer solution hydroxypropylcellulose (Hercules IncWilmington, Del.), 22% active

PVP K-120, 2-Pyrrolidinone, 1-Ethenyl-, Homopolymer (ISP TechnologiesInc., Wayne, N.J.), 100% solids

S-MAZ® 60K Flake sorbitan Monostearate Kosher (BASF, Mt. Olive, N.J.),100% solids

WITCOLATE™ WAQE sodium lauryl sulfate (Akzo Nobel IndustrialSpecialties, Chicago, Ill.), 22% active solution

SURFYNOL® 420 ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol (AirProducts & Chemical Inc, Allentown, Pa.), used as 100% solution

TWEEN®20 polyoxyethylene (20) sorbitan monolaurate (Uniqema, New Castle,Del.), 100% active

TWEEN®21 polyoxyethylene (4) sorbitan monolaurate (Uniqema, New Castle,Del.), 100% active

Sample Testing

Antifog characteristics of films were evaluated by the following method:

Ambient Testing

A sample of film was placed over the mouth of a 4 oz. jar containing 60ml of water at 50° C., and the assembly was maintained at ambienttemperature and the time elapsed until the film surface became visiblyfoggy was recorded. If no fog was found by 5 minutes elapsed time, thetest was discontinued.

Refrigerated Testing

A sample of film was placed over the mouth of a 4 oz. jar containing 60ml of water at 2-5° C. (35-40° F.). The jar was placed in a refrigeratorheld at 2-5° C., and the time elapsed until the film surface becamevisibly foggy was recorded, as well as the time until the fogsubsequently disappeared. Finally, the time at which the firstcondensation (visible droplets of water) appeared was noted.Condensation was evaluated at 1 minute, 2 minutes, 2 hours and 24 hoursafter placing the film on the jar. A notation that no fog was formed atambient and refrigerated temperatures means that no fog was visible atany of the 1-minute, 2-minute, 2-hour, or 24-hour evaluations.

Haze, which is caused by light diffused in all directions and whichresults in a loss of contrast, was also evaluated. ASTM D 1003 defineshaze as that percentage of light which in passing through deviates fromthe incident beam greater than 2.5 degrees on the average. Haze wasmeasured with a BYK Gardner “Haze Gard Plus” instrument (BYK-GardnerUSA, Columbia, Md.) using ASTM D 1003-61, procedure A.

Example 1

To produce the coating formulation, the following components were addedto 96.8 parts by weight of water under agitation:

0.128 parts by weight of a 52 wt % aqueous potassium silicate solution,

1.024 parts by weight of TEGO-WET® 251 polyether modified polysiloxanesurfactant, and

2.048 parts by weight of GLYCOLUBE® AFA-1.

The coated film was prepared as follows. PET was dried and thenmelt-extruded into a flat sheet and cooled on a chilled roll to form asubstrate layer. The temperature of the cast film was then increased bypassing the film over hot rollers (80° C.-85° C.) and heating byinfrared heaters. The film was then stretched lengthwise at a draw ratioof 3.4:1. The stretched film was then contacted with chilled rolls (15°C.-25° C.), which reduces the film temperature to minimizecrystallization and embrittlement of the film. The film was thenroll-coated on both sides with the antifog coating formulation. Wetcoating thickness, measured by an infrared gauge, was 7.4 to 9.4microns. The coated film was dried in a tenter frame in two forced airovens at about 105° C. The film was then drawn in the transversedirection at a ratio of 3.0:1 to 4.5:1 in two ovens operating at 110°C.-130° C. After drawing, the coated film was heat set for about 8seconds in three heat-setting ovens operating at between 225° C. and237° C. In a final cooldown step, the film temperature was reduced in anair oven operating at about 165° C.

Dry coating thickness was 10 to 20 nm as measured on the finished film.The haze value was 0.7. The film showed very good antifog properties, nofog being formed at ambient and refrigerated temperatures.

Example 2

To produce the coating formulation, the following components were addedto 98.6 parts by weight of water under agitation:

0.309 parts by weight of a 52 wt % aqueous potassium silicate solution,

0.58 parts by weight of TEGO-WET® 251 polyether modified polysiloxanesurfactant,

0.8 parts by weight of GLYCOLUBE® AFA-1, and

0.032 parts by weight of MX-150.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. Dry coating thickness was 10to 20 nm as measured on the finished film. The haze value was 1.32. Thefilm showed very good antifog properties, no fog being formed at ambientand refrigerated temperatures.

Example 3

To produce the coating formulation, the following components were addedto 98.4 parts by weight of water under agitation:

0.295 parts by weight of a 52 wt % aqueous potassium silicate solution,

0.4 parts by weight of TEGO-WET® 251 polyether modified polysiloxanesurfactant,

0.80 parts by weight of GLYCOLUBE® AFA-1, and

0.16 parts by weight of XX-1255Z.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. Dry coating thickness was 10to 20 nm as measured on the finished film. The haze value was 1.51. Thefilm showed very good antifog properties, no fog being formed at ambientand refrigerated temperatures.

Example 4

To produce the coating formulation, the following components were addedto 98.4 parts by weight of water under agitation:

0.295 parts by weight of a 52-wt % aqueous potassium silicate solution,

0.4 parts by weight of TEGO-WET® 251 polyether modified polysiloxanesurfactant,

0.80 parts by weight of GLYCOLUBE® AFA-1, and

0.16 parts by weight of XX-1269Z.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. Dry coating thickness was 10to 20 nm as measured on the finished film. The haze value was 1.46. Thefilm showed very good antifog properties, no fog being formed at ambientand refrigerated temperatures.

Comparative Example 5

To produce the coating formulation, the following components were addedto 99.7 parts by weight of water under agitation:

0.05 parts by weight of a 52-wt % aqueous potassium silicate solution,and

0.25 parts by weight of TEGO-WET® 251 polyether modified polysiloxanesurfactant.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film showed fair antifogproperties; fog formed at ambient temperature, but disappeared afterabout ten seconds. The haze value was 0.45. It is believed that the lackof a hydrophilic antifog agent interfered with antifog properties.

Example 6

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of TWEEN®20 polyoxyethylene (20) sorbitanmonolaurate.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film showed very goodantifog properties, no fog being formed at ambient and refrigeratedtemperatures. The haze value was 1.41.

Comparative Example 7

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution, 0.4 parts by weight of TEGO® WET 251 polyether modifiedpolysiloxane surfactant, and

0.4 parts by weight of TWEEN®21 polyoxyethylene (4) sorbitanmonolaurate.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperatures. The hazevalue was 1.17. It is believed that the TWEEN® 21 was not sufficientlyhydrophilic to provide good antifog properties.

Example 8

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of WITCOLATE™ WAQE sodium lauryl sulfate.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film showed good antifogproperties, no fog being formed at ambient temperatures. The haze valuewas 1.95.

Comparative Example 9

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of SURFYNOL® 420 ethoxylated2,4,7,9-tetramethyl-5-decyn-4,7-diol.

The coating formulation was applied to a polyethylene terephtha latefilm by manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperatures. The hazevalue was 2.22. It is believed that the SURFYNOL® 420 was notsufficiently hydrophilic to provide good antifog properties.

Comparative Example 10

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of PVP K-120, 2-Pyrrolidinone, 1-Ethenyl-,Homopolymer.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperatures. The hazevalue was 3.68. It is believed that the PVP K-120 was too high inmolecular weight to provide good antifog properties.

Comparative Example 11

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of MAZOL® GMO K Kosher glycerol Monooleate.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperatures. It isbelieved that the MAZOL® GMO K was not sufficiently hydrophilic toprovide good antifog properties.

Comparative Example 12

To produce the coating formulation, the following components were addedto 98.94 parts by weight of water under agitation:

0.265 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of S-MAZ® 60K Flake sorbitan Monostearate Kosher.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at temperatures. It is believedthat the S-MAZ® 60K was not sufficiently hydrophilic to provide goodantifog properties.

Example 13

To produce the coating formulation, the following components were addedto 98.07 parts by weight of water under agitation:

0.53 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.6 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.8 parts by weight of GLYCOLUBE® AFA-1.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film showed excellentantifog properties, no fog being formed at ambient and refrigeratedtemperatures. The haze value was 1.33.

Comparative Example 14

To produce the coating formulation, the following components were addedto 98.27 parts by weight of water under agitation:

0.53 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of PRIMAFLO® HP22 polymer solutionhydroxypropylcellulose.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperature. It isbelieved that the PRIMAFLO® HP22 was not sufficiently hydrophilic and/ortoo high in molecular weight to provide good antifog properties.

Comparative Example 15

To produce the coating formulation, the following components were addedto 98.27 parts by weight of water under agitation:

0.53 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.4 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.4 parts by weight of Poly(acrylamide-acrylic acid, Na salt) 40%carboxyl 2-propenoic acid, sodium salt, polymer with 2-propenamide.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film did not showantifog properties, fog being formed at ambient temperature. It isbelieved that the Poly(acrylamide-acrylic acid, Na salt) was too high inmolecular weight to provide good antifog properties.

Example 16

To produce the coating formulation, the following components were addedto 98.07 parts by weight of water under agitation:

0.53 parts by weight of a 52 wt % aqueous K120® potassium silicatesolution,

0.6 parts by weight of TEGO® WET 251 polyether modified polysiloxanesurfactant, and

0.8 parts by weight of BYK® 348 polyether modified dimethylpolysiloxanecopolymer.

The coating formulation was applied to a polyethylene terephthalate filmby manual drawdown using a No. 0 Meyer rod. The film showed very goodantifog properties, no fog being formed at ambient and refrigeratedtemperatures. The haze value was 1.46.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimswithout departing from the invention.

What is claimed is:
 1. A composite film comprising a polyester filmsubstrate having first and second sides, and on at least one of saidfirst and second sides a coating composition comprising an alkali metalsilicate, a wetting agent, and a hydrophilic antifog agent, wherein thehydrophilic antifog agent has a molecular weight no greater than 20,000Daltons.
 2. The composite film of claim 1, wherein the coating is onboth of the first and second sides.
 3. The composite film of claim 1,wherein the alkali metal silicate is potassium silicate.
 4. Thecomposite film of claim 1, wherein the wetting agent is a polyethermodified polysiloxane surfactant.
 5. The composite film of claim 1,wherein the alkali metal silicate is potassium silicate, the wettingagent is a polyether modified polysiloxane surfactant, and thehydrophilic antifog agent has three or more polyoxyethylene chains.
 6. Acomposite film comprising a polyester film substrate having first andsecond sides, and on at least one of said first and second sides acoating composition comprising an alkali metal silicate, a wettingagent, and a hydrophilic antifog agent, wherein the hydrophilic antifogagent comprises a compound having three or more polyoxyethylene chains.7. A method of making the composite film of claim 1, comprising thesteps of: a) providing an unoriented or monoaxially oriented polyesterfilm substrate having first and second sides; b) forming on at least oneof said first and second sides a layer of the coating compositioncomprising the alkali metal silicate, the wetting agent, and thehydrophilic antifog agent, said forming comprising contacting said atleast one side with a dispersion of the coating composition in anaqueous diluent and then evaporating the diluent; and c) subsequent tostep b), stretching the unoriented or monoaxially oriented polyesterfilm substrate to respectively monoaxially or biaxially orient thesubstrate.
 8. The method of claim 7, further comprising, after step c),d) heat setting the polyester substrate.
 9. The method of claim 7,wherein the substrate of step a) is monoaxially oriented.
 10. The methodof claim 7, wherein step b) comprises forming a layer of the coatingcomposition on both of the first and second sides.
 11. The method ofclaim 7, wherein the alkali metal silicate is potassium silicate. 12.The method of claim 7, wherein the wetting agent is a polyether modifiedpolysiloxane surfactant.
 13. The method of claim 7, wherein thehydrophilic antifog agent comprises a compound having three or morepolyoxyethylene chains.
 14. The method of claim 7, wherein the alkalimetal silicate is potassium silicate, the wetting agent is a polyethermodified polysiloxane surfactant, and the hydrophilic antifog agentcomprises a compound having a molecular weight no greater than 20,000Daltons having three or more polyoxyethylene chains.